Clock controlling method and circuit

ABSTRACT

A clock control circuit comprises a control circuit  102  for outputting a control signal for adding or subtracting a phase to a reference clock, which is an input clock or a clock generated from the input clock, on each clock period of the reference clock, and a phase adjustment circuit  101  fed with the input clock and outputting an output clock having the phase adjusted to the reference clock.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.10/237,713, filed Sep. 9, 2002, now U.S. Pat. No. 6,621,317 which inturn is a divisional of U.S. application Ser. No. 09/910,117, filed Jul.20, 2001.

FIELD OF THE INVENTION

This invention relates to a clock control circuit and a clock controlmethod.

BACKGROUND OF THE INVENTION

A PLL (phase locked loop) circuit is used in a circuit for adjusting aclock period. FIG. 27 illustrates a conventional PLL circuit. Referringto FIG. 27, a phase frequency detector (PFD) 319 receives an externalclock 324 and a signal supplied from a frequency divider 323 thatreceives an output of a voltage-controlled oscillator 322. A charge pump320 receives a up signal 325 and a down signal 326 both output from aphase frequency detector (PFD) 319 to output a voltage corresponding toa phase difference. A loop filter receives the voltage from the chargingpump 320 to output smoothed voltage which is supplied as a controlvoltage to the voltage-controlled oscillator (VCO) 322. An output clocksignal of a frequency corresponding to the control voltage from thevoltage-controlled oscillator (VCO) 322 is fed to a frequency divider323.

For example, there is proposed in JP Patent Kokai JP-A-11-284497 aprogrammable delay generator in which a ramp waveform voltage fordetermining a delay time and a threshold voltage can be generated bycircuits of the same structure and can be in independently set so thatit is capable of generating the delay time of a fractional number, anumerator and a denominator of which can be set, a frequency synthesizerwhich, by phase-interpolating output pulses of an accumulator using aprogrammable delay generator, is able to generate an adjustment-freelow-spurious output signal, a multiplication circuit employing aprogrammable delay generator, a duty ratio converter circuit employingthe programmable delay generator as an output pulse width setting delaygenerator, and a PLL frequency synthesizer having the programmable delaygenerator inserted between the frequency divider and a phase comparator.

SUMMARY OF THE DISCLOSURE

However, the conventional circuit, as shown in FIG. 27, employing a PLLcircuit and a feedback type circuit, has drawbacks that phase adjustmentoperation is time-consuming and that there exists a jitter (phase noise)proper to a feedback system.

Moreover, the above-described conventional programmable delay generatoris in need of a power source voltage generating circuit, such as athreshold voltage generating circuit, and hence the circuit scale isincreased.

It is therefore an object of the present invention to provide a clockcontrol circuit and a clock control method whereby non-integer frequencyconversion can be effected with a high degree of accuracy by asimplified configuration.

For accomplishing the above object, one aspect of the present inventionis a configuration in which a clock is input and an output clock havinga phase difference relative to the input clock, the phase obtained byadding or subtracting to or from said phase by a predetermined unitvalue of a phase differential, on each constant period, is output.

In accordance with another aspect of the present invention, a clockcontrol circuit comprises control means for outputting a control signalfor adding or subtracting to or from the phase of an output signalrelative to a reference clock, which is an input clock or a clockgenerated from the input clock, on each clock period of the referenceclock, and phase adjustment means fed with the input clock forgenerating and outputting output clock having a phase corresponding toadding or subtracting a preset unit value of a phase differential to orfrom a phase with respect to the reference clock, based on the controlsignal, hereby an output clock of a frequency in a non-integer relationto the frequency of the reference clocks can be output.

Another aspect of the present invention is a clock control circuitcomprising a frequency divider for outputting frequency-divided clockobtained on frequency dividing the input clock, a control circuit forgenerating a control signal for adding or subtracting a unit phasedifference to or from the input clock with respect to thefrequency-divided clock based on the frequency divided clock output fromthe frequency divider and a phase adjustment circuit fed with the inputclock and generating and outputting an output clock having a phaseprescribed by the control signal from the control circuit.

Another aspect of the present invention is a clock control circuitcomprising a multi-phase clock generating circuit for generating andoutputting first to nth clocks having respective different phases(multi-phase clocks) from a phase of the input clock, a selector fedwith the first to nth clocks to selectively output one of the clocks,and a control circuit fed with the input clock to generate a controlsignal sequentially selecting the first to nth clocks to send thegenerated selection signal to the selector.

Another aspect of the present invention is a clock control circuitcomprising an interpolator receiving a frequency divided signal producedby a frequency dividing circuit receiving a clock signal and a signalobtained by shifting the frequency divided signal in a preset number ofperiods of the clock to produce a signal obtained on division of atiming difference of said two input signals at a preset ratio ofinternal division; and

a control circuit for varying the value of the ratio of the internaldivision of the timing difference in said interpolator based on saidclock signals.

Another aspect of the present invention is a clock control circuitcomprising a plurality of (N) interpolators for outputting signalsobtained on dividing a timing difference of two input signals withrespective different values of a preset ratio of internal division;wherein of first to nth clocks with respective different phases, twoclocks, that is the Ith and the (I+1)st clocks, where I is an integerfrom 1 to N, with N+1 being 1, are input to the Ith interpolator.

In accordance with another aspect of the present invention, theinterpolator comprises a logic circuit fed with first and second inputsignals to output a result of preset logical processing of said firstand second input signals;

a first switching device connected across a first power source and aninternal node, said first switching device being fed at a controlterminal thereof with an output signal of said logic circuit and beingturned on when said first and second input signals are both of a firstvalue;

a buffer circuit having an input terminal connected to said internalnode and having an output logical value changed on inversion of relativemagnitudes of the terminal voltage of the capacitance of said internalnode and a threshold value;

a plurality of serial circuits connected across said internal node and asecond power source in parallel, each of said serial circuits being madeup of a second switching device turned on when said first input signalis of a second value, said third switch device turned on or off based ona control signal from said control circuit, and a first constant currentsource; and

a plurality of serial circuits connected across said internal node and asecond power source in parallel, each of said serial circuits being madeup of a fourth switching device turned on in common when said firstinput signal is of a second value, said fifth switching device turned onor off based on a control signal from said control circuit, and aconstant current source.

In accordance with another aspect of the present invention, saidinterpolator comprises a logic circuit receiving first and second inputsignals to output results of preset logical processing of said first andsecond input signals;

a first switching device connected across a first power source and aninternal node, said first switching device being fed at a controlterminal thereof with an output signal of said logic circuit and beingturned on when said first and second input signals are both of a firstvalue; and

a buffer circuit having an input end connected to said internal node andhaving an output logical value changed on inversion of the relativemagnitudes of the terminal voltage of the capacitance of said internalnode and a threshold value;

a plurality of serial circuits connected across said internal node and asecond power source in parallel, each of said serial circuits being madeup of a second switching device turned on when said first input signalis of a second value, said third switch device turned on or off based ona control signal from said control circuit, and a first constant currentsource;

a plurality of serial circuits connected across said internal node and asecond power source in parallel, each of said serial circuits being madeup of a fourth switching device turned on in common when said firstinput signal is of a second value, said fifth switching device turned onor off based on a control signal from said control circuit, and aconstant current source; and

a plurality of serial circuits connected across said internal node andthe second power source in parallel, each said serial circuit being madeup of a sixth switching device and a capacitor device; the value of saidcapacitance attached to said internal node being determined by a periodcontrol signal supplied to a control terminal of said sixth switchingdevice.

In accordance with another aspect of the present invention, a clockcontrol method comprises the steps of generating an output clock havinga phase relative to a reference clock by adding or subtracting to orfrom said phase by a predetermined unit value of a phase differential oneach clock period of said reference clock, said reference clock being aninput clock or a clock derived from the input clock; and outputting saidoutput clock.

Still other objects and advantages of the present invention will becomereadily apparent to those skilled in this art from the followingdetailed description, wherein only the preferred embodiment of theinvention is shown and described, simply by way of illustration of thebest mode contemplated of carrying out this invention. As will berealized, the invention is capable of other and different embodiments,and its several details are capable of modifications in various obviousrespects, all without departing from the invention. Accordingly, thedrawing and description are to be regarded as illustrative in nature,and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a configuration of a first embodiment of the presentinvention.

FIG. 2 is a timing chart for illustrating operation of the firstembodiment of the present invention.

FIG. 3 shows a configuration of a second embodiment of the presentinvention.

FIG. 4 shows a configuration of a third embodiment of the presentinvention.

FIG. 5 shows an illustrative structure of a multi-phase clock generatingcircuit of a third embodiment of the present invention.

FIG. 6 shows an illustrative structure of the four-phase clockgenerating circuit of the third embodiment of the present invention.

FIG. 7 is a timing diagram for illustrating the operation of thefour-phase clock generating circuit of the third embodiment of thepresent invention.

FIG. 8 shows an illustrative structure of a circuit configuration of atiming difference division circuit (interpolator) of FIG. 6.

FIG. 9 is a timing diagram for illustrating the operation of a timingdifference division circuit (interpolator) of FIG. 6.

FIG. 10 shows a modification of a timing difference division circuit(interpolator).

FIG. 11 illustrates an operating principle of the timing differencedivision circuit (interpolator).

FIG. 12 shows a first embodiment of the circuit configuration of avariable internal division ratio interpolator used in an embodiment ofthe present invention.

FIG. 13 shows a second embodiment of the circuit configuration of avariable internal division ratio interpolator used in an embodiment orthe present invention.

FIG. 14 shows a third embodiment of the circuit configuration of avariable internal division ratio interpolator used in an embodiment ofthe present invention.

FIG. 15 shows a fourth embodiment of the circuit configuration of avariable internal division ratio interpolator used in an embodiment ofthe present invention.

FIG. 16 shows the configuration of a fourth embodiment of the presentinvention.

FIG. 17 is a timing chart for illustrating the operation of the fourthembodiment of the present invention.

FIG. 18 shows the configuration of a fifth embodiment of the presentinvention.

FIG. 19 is a timing chart for illustrating the operation of the fifthembodiment of the present invention.

FIG. 20 shows the configuration of a sixth embodiment of the presentinvention.

FIG. 21 is a timing chart for illustrating the operation of the sixthembodiment of the present invention.

FIG. 22 shows a configuration of a seventh embodiment of the presentinvention.

FIG. 23 shows a configuration of an eighth embodiment of the presentinvention.

FIG. 24 shows a configuration of a ninth embodiment of the presentinvention.

FIG. 25 shows a layout of a 16-equi-division interpolator used in theembodiments of the present invention.

FIG. 26 is a waveform diagram showing the results of simulation of theoutput of the phase adjustment circuit employing the q6-equi-divisioninterpolator in the embodiments of the present invention.

FIG. 27 shows a typical conventional clock control circuit.

PREFERRED EMBODIMENTS OF THE INVENTION

Preferred embodiments of the present invention are described below. In apreferred embodiment of the present invention, a clock control circuitcomprises control circuit (102 of FIG. 1) for outputting a selectioncontrol signal for selecting incrementing (adding) or decrementing(subtracting) to or from a phase relative to a reference clock by apredetermined unit value of a phase differential on each reference clockcycle, which is an input clock or a clock generated from an input clock;and a phase adjustment circuit (101 of FIG. 1) fed with the input clockand generating an output clock having a phase corresponding toincrementing or decrementing a predetermined unit phase value of a phasedifferential with respect to the reference clock, based on the controlsignal, whereby an output clock of a frequency in a non-integer relationwith respect to the frequency of the reference clock can be output.

In another preferred embodiment of the present invention, a clockcomprises a frequency divider (103 of FIG. 3) for outputtingfrequency-divided clock obtained by frequency dividing the input clock,a control circuit (102 of FIG. 3) for generating a control signal foradding or subtracting to or from a phase by a unit phase differentialrelative to the input clock with respect to the frequency-divided clocksbased on the frequency divided clocks' output from the frequencydivider, and a phase adjustment circuit (101 of FIG. 3) fed with theinput clock and generating and outputting an output clock having a phaseprescribed by the control signal from the control circuit.

In another preferred embodiment of the present invention, a clockcontrol circuit comprises a multi-phase clock generating circuit (201 ofFIG. 4) for generating and outputting first to nth clocks havingrespective difference phases from the phase of the input clock(multi-phase clocks), and a selector (203 of FIG. 4) fed with the firstto nth clocks to selectively output one of the clocks and a controlcircuit (202 of FIG. 4) fed with the input clock to generate a controlsignal sequentially selecting the first to nth clocks to send thegenerated selection signal to the selector.

According to the present invention, the phase adjustment circuit iscomprises an interpolator for dividing timing difference of two inputsignals to output a signal. There is provided a control circuitoperating so that a signal obtained on frequency division of the clocksignals and a signal shifted preset clock periods are input to theinterpolator and the timing difference division ratio in theinterpolator is changed based oil the clock signals.

Alternatively, there may be provided plural interpolators, each of whichoutputs a signal, a propagation delay of said signal corresponding tothe division of timing difference between two input signals. The valuesof timing difference division ratio in the plural interpolators are setto respective different values. Plural sets of two clocks of plural (N)clocks of different phase may be input to the plural interpolators sothat both end side clocks, that is the first and Nth clocks are providedto one interpolator.

In another preferred embodiment of the present invention, a clockcontrol circuit comprises a multi-phase multiplication clock generatingcircuit (10 of FIG. 20) for generating first to nth clocks, phases ofwhich are different (termed multi-phase multiplication clocks) obtainedon multiplying input clock based on the input clock,

a switch (20 of FIG. 20 for selecting two of the first to nth clocksoutput from the multi-phase multiplication clock generating circuit,

an interpolator (30 of FIG. 20) fed with the two clock signals selectedand output by the switch to output a signal corresponding to division ofthe two clock signals, with a ratio of the internal division beingvariably set, and

a control circuit (40 of FIG. 20) for outputting a switching signal forthe switch and a control signal for variably setting the ratio of theinternal division of the timing difference of the interpolator.

In another preferred embodiment of the present invention, a clockcontrol circuit comprises a multi-phase multiplication clock generatingcircuit (10 of FIG. 22) for generating first to nth clocks of respectivedifferent phases(multi-phase multiplication clocks) obtained onmultiplying frequency divided input clock based on the input clock,

a switch (20 of FIG. 22) for selecting two sets each of two neighboringones of the first to nth clocks output from the multi-phasemultiplication clock generating circuit,

a first interpolator (30 ₁ of FIG. 22) fed with the first set of twoclocks output from the switch to output a signal, a propagation delay ofsaid signal corresponding to division of the timing difference of thetwo clock signals,

a second interpolator (30 ₂ of FIG. 22) fed with the second set of twoclocks output from the switch to output a signal, a propagation delay ofsaid signal corresponding to division of the timing difference of thetwo clock signals,

a third interpolator (30 ₃ of FIG. 22) fed with outputs of the first andsecond interpolators to output a signal, a propagation delay of saidsignal corresponding to division of the timing difference of the twooutputs, and

a control circuit (40 of FIG. 22) for outputting a switching signal forthe switch and a control signal for variably setting ratio of theinternal division of the timing difference of the interpolators. Theratio of the internal division of the timing difference of at least oneof the first to third interpolators can be set variably.

The multi-phase multiplication circuit comprises a frequency divider (2of FIG. 5) for frequency dividing an input clock to generate and outputa plurality of clocks of different phases (multi-phase clocks), a perioddetection circuit (6 of FIG. 5) for detecting a period of the inputclock and a multi-phase clock multiplication circuit (5 of FIG. 5) fedwith the multi-phase clocks corresponding to frequency multiplied clocksto generate multi-phase clocks corresponding to multiplication of theclocks.

The multi-phase clock multiplication circuit preferably comprises aplurality of timing difference division circuits (4 a 1 to 4 a 8 of FIG.6) for outputting a signal corresponding to the division of the timingdifference of two inputs and a plurality of multiplexing circuits (4 b 1to 4 b 4 of FIG. 6) multiplexing two outputs of the timing differencedivision circuits to output the resulting multiplexed signals.

The timing difference division circuit include timing differencedivision circuits (4 a 1, 4 a 3, 4 a 5, 4 a 7 of FIG. 6) fed with clocksof the same phase and timing difference division circuits (4 a 2, 4 a 4,4 a 6, 4 a 8 of FIG. 6) fed with two clocks of neighboring phases.

The multi-phase clock multiplication circuits (5) preferably comprises2n timing difference division circuits for outputting signalscorresponding to division of the timing difference of two inputs,wherein

(2I−1)st timing difference division circuits (4 a 1 to 4 a 8 of FIG. 6),where 1≦I≦n, are fed with the same Ith clocks as the two inputs,

2Ith timing difference division circuits (4 a 2, 4 a 4, 4 a 6, 4 a 8 ofFIG. 6), where 1≦I≦n, are fed with the Ith clocks and with the (I+1 modn)th clocks, where mod denotes remainder calculations and I+1 mod nmeans the remainder of the division of (I+1) with m,

2n pulse width correction circuits (4 c 1 to 4 c 8 of FIG. 6) fed withoutputs of Jth timing difference division circuits, where 1≦J≦2n, andwith outputs of (J+2 mod n)th timing difference division circuits, whereJ+2 mod n means the remainder of division of J+2 with n, and

n multiplexing circuits (4 b 1 to 4 b 4 of FIG. 6) fed with outputs ofKth pulse width correction circuit, where 1≦K≦n, and with outputs of the(K+n)th pulse width correction circuits.

In another preferred embodiment of the present invention, a clockcontrol circuit comprises a frequency divider (60 of FIG. 23) fed withinput clock to generate two sets of clocks of respective differentphases obtained on frequency division of the input clock,

a first interpolator (30 ₁ of FIG. 23) fed with the first set of twoclocks output from the frequency divider to output a signal, apropagation delay of said output signal corresponding to division oftiming difference of the two clock signals,

a second interpolator (30 ₂ of FIG. 23) fed with the second set of twoclocks output from the frequency divider to output a signal, apropagation delay of said output signal corresponding to division oftiming difference of the two clock signals,

a third interpolator (30 ₃ of FIG. 23) fed with outputs of the first andsecond interpolators to output a signal, a propagation delay of saidoutput signal corresponding to division of timing difference of the twooutputs, with the ratio of the internal division of the timingdifference of at least one of the first to third interpolators beingvariably set, and

a control circuit (40 of FIG. 23) for outputting a switching signal forthe switch and a control signal for variably setting the ratio of theinternal division of the timing difference of the interpolators.

In another preferred embodiment of the present invention, a clockcontrol circuit comprises a multi-phase multiplication clock generatingcircuit (10 of FIG. 24) for generating plural clocks of respectivedifferent phases obtained on frequency multiplying input clock based onthe input clock,

a plurality of interpolators (30 _(l) to 30 _(n) of FIG. 24) fed withtwo clocks of neighboring phases of the plural clocks output from themulti-phase multiplication clock generating circuit to output signals,propagation delay of said signals corresponding to division withrespective different values of ratio of internal division of timingdifference of the two clocks and

a synthesis unit (50 of FIG. 24) fed with outputs of the pluralinterpolators to multiplex the outputs of the interpolators to output aresulting sole output signal.

In this embodiment, the multi-phase multiplication clock generatingcircuit generates N phase clocks, where N is a preset positive integer,M of the interpolators are provided, where M is a positive integer suchthat M≦N.

The ith interpolator is fed with ith and (i+1)st clocks, where i is aninteger from 1 to M while the (n+1)st clock is treated as a first clock.A value of ratio of internal division dividing timing difference of twoinput signals in each of the interpolators is so set that the ratiovalue of the (i+1)st interpolator is larger or smaller than that of theith interpolator by a preset unit step.

M-phase clocks are output from the M interpolators and wherein M-tupledclocks are output from the synthesis unit. The internal division ratiodividing the timing different of the two interpolators is of a fixedvalue.

In the above-described embodiment of the present invention, shown inFIGS. 12 to 15, the interpolator comprises

a logic circuit (NAND01) fed with first and second input signals tooutput results of preset logical processing of the first and secondinput signals,

a first switching device (MP1) connected across a first power source andan internal node (N31), the first switching device being fed at acontrol terminal thereof with an output signal of the logic circuit andbeing turned on when the first and second input signals are both of afirst value,

a buffer circuit (INV3) having an input end connected to the internalnode and having an output logical value changed on inversion of therelative magnitudes of the terminal voltage of the capacitance of theinternal node and a threshold value,

a plurality of serial circuits connected across the internal node and asecond power source in parallel, each of the serial circuits being madeup of a second switching device (MN11) turned on when the first inputsignal (IN1)is of a second value, the third switch device (MN21) turnedon or off based on a control signal (PH) from the control circuit (40 ofFIG. 20), and a constant current source (I₀),

a plurality of serial(series) circuits connected across the internalnode and a second power source in parallel, each of the serial circuitsbeing made up of a fourth switching device (MN12) turned on in commonwhen the first input signal is of a second value, the fifth switchingdevice (MN22) turned on or off based on a control signal from thecontrol circuit, and a constant current source (I₀).

The third switching device (MN21) may be connected on the site of theinternal node (N31),with the second switching device (MN11) then beingconnected to the side of the constant current source (I₀) in aninterchanging fashion. The fourth switching device (MN12) may, ofcourse, be interchanged with the fifth switching device (MN22).

A plurality of serial circuits, each made up of a sixth switching deviceand a capacitor (MN31 to MN34 and CAP11 to CAP14), are connected inparallel across the internal node (N31) and the second power source. Thevalue of capacitance to be attached to the internal node is selectivelydetermined by the periodic control signal 7 supplied to the controlterminal of the group of the sixth switching devices (MN31 to MN34).

For more detailed explanation of a preferred embodiment of the presentinvention, certain preferred embodiments of the present invention willbe explained with reference to the drawings.

FIG. 1 illustrates a structure of a first embodiment of the presentinvention. Referring to FIG. 1, the first embodiment of the presentinvention comprises a phase adjustment circuit 101 that receives aninput clock and generate an output clock having a phase adjusted withrespect to a reference clock as which is used the input clock or asignal derived from the input clock and a control circuit 102 thatreceives the input clock and the code information to output a selectionsignal to the phase adjustment circuit 101.

Preferably, the phase adjustment circuit 101 comprises in interpolatorin which a interior division ratio of timing difference is variably setin a programmable way.

The control circuit 102 comprises an addition circuit for incrementing apreset unit m (m=1, 2, 3, . . . ) from an initial value 0 (0, m, 2m, 3m,. . . ) each time it is fed with the input clock. The preset value m isset by a code signal input to the control circuit 102 from outside.

The control circuit 102 may comprises a subtraction circuit fordecrementing a preset unit m (m=1, 2, 3, . . . ) e.g., from the initialvalue N each time it is fed with an input clock. A result of thesubtraction is decoded and a selection signal (control signal)corresponding to the result of the subtraction is supplied to the phaseadjustment circuit 101. The value of the preset unit m is set by a codesignal input from outside to the control circuit 102.

Based on the selection signal from the control circuit 102, the phaseadjustment circuit 101 outputs a signal comprising pulse edges withphase differences of 0, ΔΦ, 2ΔΦ, 3ΔΦ, . . . , (n−1)ΔΦ, nΔΦ, . . . , fromcorresponding edges, such as rising edges of an input clock with aperiod tCK, where ΔΦ is a unit phase differential which is determined bythe selection signal from the control circuit 102. It is noted that nΔΦis equivalent to phase difference 0.

With the unit phase difference ΔΦ, for the selection signal “m” from thecontrol circuit 102 being “1”, the unit phase difference in the phaseadjustment circuit 101 is mΔΦ, such that signal with phase differencesof 0, mΔΦ, 2mΔΦ, 3mΔΦ, . . . , (n−1)mΔΦ, nmΔΦ, . . . is output from oneinput clock to another. It is noted that, with the unit phase differenceΔΦ of tCK/n, nmΔΦ is equivalent to the phase difference 0.

Referring to FIG. 2, showing the operating principle of the firstembodiment of the present invention, a phase difference of an outputclock relative to a rising edge of an input clock in a clock cycle 1 is0,

a phase difference of the output clock relative to a rising edge of theinput clock in a clock cycle 2 is ΔΦ and

a phase difference of the output clock relative to a rising edge of theinput clock in a clock cycle 3 is 2ΔΦ, and so on.

A period of the output clock is tCK+ΔΦ, such that a frequency f=1/tCK ofthe input clock hiving a clock period tCK is frequency-converted into afrequency=1/(tCK+ΔΦ). A clock period is frequency-converted with a valueother than integer ratio(non-integer value) (=1+ΔΦ/tCK) of the inputclock frequency.

When the output clock and the input clock are interchanged in FIG. 2,the result is the timing operation of the control circuit 102 made up ofa subtraction unit and a decoder. If the control circuit 102 comprises asubtraction unit, the phase differences of the output clock relative tothe rising edge of the input clock is −ΔΦ, −2ΔΦ, . . . .

A second embodiment of the present invention is now explained. FIG. 3illustrates a structure of the second embodiment of the presentinvention. Referring to FIG. 3, the second embodiment includes afrequency divider 103 for frequency dividing input clock, a controlcircuit 102 and a phase adjustment circuit 101. The frequency divider103 is fed with an input clock to frequency divide the input clock foroutputting a frequency divided clock.

The control circuit 102 comprises an adder for incrementing code signalsm (m=1, 2, 3, . . . ) from an initial value 0 to (0, 2m, 3m, . . . )each time it is fed with the input clock, and a decoder for decoding theoutput of the adder to output a selection signal associated with thedecoded value to the phase adjustment circuit 101.

With a unit phase difference of ΔΦ, the phase adjustment circuit 101outputs a signal comprising pulse edges with phase differences of 0,mΔΦ, 2mΔΦ, 3mΔΦ, . . . , (n−1)mΔΦ, nmΔΦ, . . . , from correspondingedges of the input clock, based on the selection signal from the controlcircuit 102, from one input clock to another. It is noted that, with theunit phase difference ΔΦ equal to tCK/n, nmΔΦ is equivalent to phasedifference 0.

A frequency f=b 1/tCK of the input clock with a period of tCK isconverted into a frequency=1/(tCK+ΔΦ), with the period of the outputclock being tCK+ΔΦ, such that the clock period can be changed to a valueother than an integer ratio.

In the present second embodiment, the control circuit 102 may, ofcourse, be made up of a subtraction unit and a decoder.

A third embodiment of the present invention is now explained. FIG. 4illustrates a structure of the third embodiment of the presentinvention. Referring to FIG. 4, the present third embodiment includes amulti-phase clock generator 201, a selector 202 and a control circuit203 for supplying a selection signal to the selector 202.

The multi-phase clock generator 201 output nth clocks, a timing (phase)difference between clocks with neighboring phases clocks is ΔΦ=tCK/n.

The first to the nth clocks are selected in a cyclic way by the selector202, under control by the control circuit 203, such that

the first clock is selected in a clock cycle 1, with the phasedifference of the output clock relative to the rising edge of the inputclock being 0;

the second clock is selected in a clock cycle 2, with the phasedifference of the output clock relative to the rising edge of the inputclock being ΔΦ; and

the third clock is selected in a clock cycle 3, with the phasedifference of the output clock relative to the rising edge of the inputclock being 2ΔΦ, and so on.

The period of the output clock is tCK+ΔΦ, such that the frequencyf=1/tCK of the input clock with the period tCK is converted to thefrequency=(tCK+ΔΦ), to render it possible to convert the clock periodwith a value other than an integer (=1+ΔΦ/tCK).

The above-described embodiment of the present invention will beexplained in further detail. In the following, the present embodiment isexplained in detail based on the circuit structure shown in FIG. 4, inconsideration of a sequence of explanation of the timing differencecircuit (interpolator) characteristic of the present invention.

FIG. 5 illustrates an example of a structure of the multi-phase clockgenerator 201 shown in FIG. 4. FIG. 6 shows a specified embodiment ofthe structure of a multiplication interpolator embodying the presentinvention as a multi-phase clock generator 201 generating four-phaseclocks.

Referring to FIG. 5, the four-phase clock generator includes a ¼frequency divider 2 for frequency-dividing an input clock 1 by four tooutput four-phase clocks Q1 to Q4, a n-stage cascade-connectedfour-phase clock multiplication circuits(termed frequency doublingcircuits) 51 to 5 n and a period detection circuit 6. Meanwhile, thenumber of the stages n of the four-phase clock multiplication circuitsis arbitrary.

The ¼ frequency divider 2 divides a frequency of the input clock by ¼ togenerate four-phase clocks Q1 to Q4, which then are multiplied by thefour-phase clock multiplication circuit 51 to generate four-phase clocksQ11 to Q14. Similarly, four-phase clocks Qn1 to Qn4 are obtained by thefour-phase clock multiplication circuit 5 n by 2 n frequencymultiplication.

The period detection circuit 6 is made up of a fixed number of stages ofring oscillators and a counter, both bot shown. During one clock period,the number of oscillations of the ring oscillator is counted by thecounter and a control signal 7 corresponding to the number of counts isoutput to adjust a load in the four-phase clock multiplication circuit5. This period detection circuit 6 operates to eliminate fluctuations indevice characteristics and in the operating range of the clock period.

FIG. 6 a illustrates a structure of the four-phase clock multiplicationcircuit 5 shown in FIG. 5. Meanwhile, the four-phase clockmultiplication circuits 51 to 5 n shown in FIG. 5 are of the samestructure. Referring to FIG. 6 a, this four-phase clock multiplicationcircuit 5 is made up of eight timing difference division circuits 4 a 1to 4 a 8, eight pulse width correction circuits 4 c 1 to 4 c 8 and fourmultiplexing circuits 4 b 1 to 4 b 4. FIG. 6 b shows a structure of apulse width correction circuit 4 c, comprised of a NAND circuit 16 fedwith a signal corresponding to a second input complemented by theinverter 17 and with a first input. FIG. 6 c shows a structure of themultiplexing circuit 4 b comprised of a two-input NAND circuit 18.

FIG. 7 illustrates signal waveforms diagram for explaining operationaltiming of the four-phase clock multiplication circuit 5 shown in FIG. 6.A rise timing of the clock T21 is determined by an internal delay of thetiming difference division circuit 4 a 1 from a rising edge of the clockQ(n−1)1, whilst a rise timing the clock T22 is determined by a timingdivision of a difference between a rise timing of the clock Q(n−1) and arise timing of the clock Q(n−1)2, and an internal delay of in the timingdifference division circuit 4 a 2.

Similarly, rise timing of the clock T26 is determined by a timingdivision of a difference between a rise timing of the clock Q(n−1)3 anda rise timing of the clock Q(n−1)4 and the internal delay in the timingdifference division circuit 4 a 2,

a rise timing of the clock T27 is determined by the internal delay of arise timing of the clock Q(n−1)2 in the timing difference divisioncircuit 4 a 7 and

a rising edge of the clock T28 is determined by a timing division of adifference between a rise timing of the clock Q(n−1)4 and a rise timingof the clock Q(n−1)1 and the internal delay in the timing differencedivision circuit 4 a 8.

The clocks T21 and T23 are fed to the pulse width correction circuit 4 c1 which then outputs a pulse P21 having a falling edge determined by theclock T21 and a pulse P21 having a rising edge determined by the clockT23. By a similar sequence of operations, pulses P22 to P28 aregenerated, with the clocks P21 to P28 being duty 25% eight-phase pulses,evenly spaced by phase 45°. The clock P25, spaced by 180° from the clockP21, is multiplexed and inverted by the multiplexing circuit 4 b 1 andoutput as a duty 25% clock Qn1.

In similar manner, clocks Qn2 to QN4 are generated. The clocks Qn1 toQN4 become duty 50% four-phase pulses, equally-spaced by 90°. The clocksQn1 to QN4 are frequency multiplied by a factor of two in the course ofgenerating the clocks Qn1 to Qn4 from the Q(n−1)1 to Q(n−)4.

FIG. 8 a and FIG. 8 b illustrate typical structures of the timingdifference division circuits 4 a 1 and 4 a 2, respectively, shown inFIG. 7. These circuits are of the same structure and differ as towhether the two inputs are the same signal or two neighboring signalsare input. That is, the timing difference division circuits 4 a 1 and 4a 2 are the same, in structure except that the same input Q(n−1)1 isinput to a two-input NOR 51 in the timing difference division circuit 4a 1 whereas Q(n−0)1 and Q(n−1)2 are input to the two-input NOR 61. Thetwo-input NORs 51, and 61 are comprised of two P-channel MOS transistorsconnected in series across the power source VDD and an output end andare connected in parallel across and to the gate of which input signalsIN1, IN2 are fed, and two N-channel MOS transistors connected inparallel across an output terminal and the ground and to the gates ofwhich are fed input signals IN1, IN2.

An internal node N51 (N61) as an output node of the two-input NOR 51(NOR 61) is connected to an input terminal of an inverter INV51 (INV61).Across the internal node and the ground are connected, in parallel, acircuit comprised of a serial connection of a N-channel MOS transistorMN 51 and a capacitor CAP 51, a circuit comprised of a serial connectionof a N-channel MOS transistor MN 52 and a capacitor CAP 52 and a circuitcomprised of a serial connection of a N-channel MOS transistor MN53 anda capacitor CAP 53. The gates of the respective MOS transistors MN51 toMN53 are fed with control signals 7 from the period detection circuit 6so as to be thereby turned on or off. The gate widths of the MOStransistors MN51 to MN53 and the capacitors CAP 51 to CAP 53 arecontrolled to a size ratio of for example, 1:2:4, with the clock periodbeing set by adjusting the load connected to the common node in eightstages based on the control signal 7 output from the period detectioncircuit 6 (see FIG. 5).

FIG. 9 shows a timing diagram for explaining the operation of the timingdifference division circuits 4 a 1 and 4 a 2.

As for the timing difference division circuit 4 a 1, electrical chargeof the node N51 is extracted through an N-channel MOS transistor of theNOR 51 and, as a potential of the node N51 has reached a threshold valueof the inverter N51, the clock T21 as an output of the inverter INV51rises.

Assuming that a value of the electrical charge of the node N51, thatneed to be extracted when the threshold value of the inverter INV 51 isreached, is CV, where C and V denote capacitance and voltage,respectively, and a discharge current by the N-channel MOS transistor ofNOR 51 is I, the electrical charge CV is discharged with a current value2I as from the rising of the clock Q(n−1)1.

So, the time CV/2I denotes a timing difference (propagation delay time)as from the rising edge of the clock Q(n−1) until the rising of theclock T21. With the clock Q(n−1)1 at Low level(logic low), the outputside node N51 of the two-output NOR 51 is charged to High level(logichigh), with the output clock of the inverter INV 51 falls to Low level.

As for the timing difference division circuit 4 a 2, the electricalcharge at the node N61 are extracted to NOR 61 during the time as from arising edge of the clock Q(n−1)1 until time tCKn (tCKn=clock period).When a potential of the node N61 has reached a threshold value of theinverter INV 61, as from a rising edge of the Q(n−1)2, the edge of theclock T22 rises.

If the electrical charge of the node N61 is CV and a discharge currentof the NMOS transistor of the two-input NOR 61 is I, and the electricalcharge CV is extracted from a rising edge of the clock Q(n−1)1 with thecurrent I during time of tCKn, and with the current 2I for the remainingtime, the time

 tCKn+(CV−tCKn·I)/2 I=CV/2 I+tCKn/2  (1)

denotes the timing difference as from the rising edge of the clockQ(n−1) until the rising edge of the clock T22.

That is, a difference of rise timings between clocks T22 and T21 istCKn/2.

If both the clock Q(n−1)1 and Q(n−1)2 are at Low level and the outputside node N61 of the two-input NOR 61 is charged to High level from thepower source through the PMOS transistor of NOR 61, the clock T22 rises.

The same holds for the clocks T22 to T28, with the rising timingsdifference of the clocks T21 to t28 being each tCKn/2.

The pulse correction circuits 4 c 1 to 4 c 8 (FIG. 6) generate duty 25%eight-phase pulses P21 to P28, dephased each 45° (see FIG. 7).

The multiplexing circuits 4 b 1 to 4 b 4 (see FIG. 6) generate duty 50%four-phase pulses Qn 1 to Qn 4, dephased each by 90°, as shown in FIG.7.

If clocks Qn 1 to Qn 4 of FIG. 7 are output from the four-phase clockgenerator 201, the selector 203, fed with Qn 1 to Qn 4, sequentiallyselects and outputs the clocks Qn 1 to Qn 4, in a sequence of the Qn 1,Qn 2, Qn 3 and Qn 4 under control by a selection signal from the controlcircuit 202. With a period T of the clocks being Qn 1 to Qn 4, clockwith a period of T(1+¼) are output from the selector 203.

FIG. 10 shows another embodiment of the timing difference divisioncircuit used in the four-phase clock multiplication circuit shown inFIG. 6 etc. Referring to FIG. 10, in the timing difference divisioncircuit, a logical OR circuit OR1 receives a first and second inputsignals IN1, IN2.

A P-channel MOS transistor MP1 is connected across the power source VCCand an internal node N26 and a gate of MOS transistor MP1 is fed with anoutput signal of the logical OR circuit OR1.

An inverter INV3 has its input terminal connected to the internal nodeN26 for inverting and outputting a potential of the internal node N26.

N-channel MOS transistors MN1, MN2, have drains, gates and sourcesconnected to the internal node N26, fed with the first and second inputsignals IN1, IN2 and connected to a constant current source I₀,respectively.

Across the internal node N26 and the ground are connected switchingdevices MN11 to MN15, comprised of N-channel MOS transistors, and thecapacitors CAP 11 to CAP15.

To control terminals, (gate terminals) of the switching devices MN11 toMN15, comprised of N-channel MOS transistors, are coupled controlsignals 7 output from the period detection circuit 6 of FIG. 5, as inthe case of the timing difference division circuits explained withreference to FIG. 8.

The switching devices MN11 to MN15 are controlled on or off depending onvalue of the control signal 7 to decide capacitance value to be attachedto the internal node N26.

The capacitance ratio of the capacitors CAP 11 to CAP15 is set to suchas 16:8:4:2:1, with the ratios of the gate widths (W) to the gatelengths (L) of the N-channel MOS transistors MN11 to MN15 being16:8:4:2:1.

If the first and second input signals IN1, IN2 are at Low level, inoutput of the OR circuit OR1 is low, such that the P channel MOStransistor MP1 is turned on to charge the internal node N26 to the powersource potential, with the output of the inverter INV3 then being at Lowlevel.

If one or both of the first and second input signals IN1, 1N2 is or areat High level, an output of the logical OR circuit OR1 changes to Highlevel, and the P-channel MOS transistor MP1 is tuned off, so that thepower source path of the power source Vcc and the internal node N26 isturned OFF.

On the other hand, one or both of the N-channel MOS transistors MN1 andMN2 are turned ON to discharge the internal node N26 so that thepotential of the internal node N26 starts to be decreased from the powersource potential. When the potential of the internal node N26 falls tobelow the threshold voltage of the inverter INV3, an output of theinverter INV3 rises from Low level to High level.

FIG. 11 illustrates operation of the timing difference division circuitTMD shown in FIGS. 8 and 10. Referring to FIG. 11 a, first one of threetiming difference division circuits (TMD) is fed at its two inputs withthe same input signal IN1 to output an output signal OUT1, while secondtiming difference division circuit (TMD) is fed at its two inputs withinput signals IN1 and IN2 to output an output signal OUT2 and thirdtiming difference division circuits (TMD) is fed at its two inputs withthe same input signal IN2 to output an output signal OUT3.

Of these, the second timing difference division circuit (TMD), fed withthe input signals IN1, IN2 to output the output signal OUT2, correspondsto the structure of the timing difference division circuit of FIG. 8 b.

The timing difference division circuit (TMD) fed with IN1 in common andthe timing difference division circuit (TMD) fed with IN2 in common arefed with the same signal in FIG. 8 a and corresponds to the structure ofthe timing difference division circuit 4 a 2 of FIG. 8 a.

FIG. 11 b shows output signals OUT1 to OUT3 of the first to third timingdifference division circuits, fed with the input signals IN1, IN2 of thetiming difference T, and changes A1 to A3 of the internal nodes of thefirst to third timing difference division circuits.

For ease of understanding, it is assumed that the internal node ischarged from an electrical potential 0 and that the output signal ischanged from low to High level when the threshold value Vt is exceeded.

Referring to FIG. 11 b, there is timing difference between the inputsignals IN1 and IN2, the first timing difference division circuit TMDoutputs an output signal OUT1 with a delay time(propagation delay) t1,the third timing difference division circuit TMD outputs an outputsignal OUT3 with a delay time t3 and the second timing differencedivision circuit TMD outputs an output signal OUT2 with a delay time t2,with the delay time t2 being a value corresponding to internal divisionof the delay time t1 and the delay time t3.

Meanwhile,t 1=CV/2I,t 2=T+(CV−IT)/(2I)−T/2+CV/2I  (2).

On the other hand, T+CV/2I (see FIG. 11 c), provided that electricalcharge discharged until the threshold value of a buffer circuit(inverter) to which is connected the inner node are denoted CV.

The structure of an interpolator, used in e.g., the phase adjustmentcircuit 101 in the embodiment of the present invention and in which theratio of internal division of the timing differences of the two inputsignals can be variably set, is explained.

FIG. 12 illustrates a structure of an interpolator forming the phaseadjustment circuit 101 and in which a internal division ratio of timingdifference can be variably set such as in a programmable manner.

Referring to FIG. 12, in this interpolator, a P-channel MOS transistorMP1 has a source and a drain connected respectively to the power sourceVcc and to a internal node N31, respectively, and having a gate fed withan output signal of a NAND circuit NAND 01 that receives a first andsecond input signals IN1, IN2.

A inverter circuit INV3 of which input terminal is connected to theinternal node N31, switches a logical value of an output signal whenrelation of magnitude of the internal node potential and a thresholdpotential value of the inverter circuit INV3 are changed.

Inverter circuits INV1, INV2 have input terminals connected respectivelyto the first and second input signals IN1, IN2.

16 N-channel MOS transistors MN11 ₁ to MN11 ₁₆ have drains connected incommon to the internal node N31 and have gates connected in common to anoutput of the inverter circuit INV1.

16 N-channel MOS transistors (switching devices) MN12 ₁ to MN12 ₁₆ havedrains connected in common to the internal node N31 and gates connectedin common to an output of the inverter circuit INV2. 16 N-channel MOStransistors MN21 ₁ to MN21 ₁₆ (switching devices) have drains connectedto the sources of N-channel MOS transistors MN11 ₁ to MN11 ₁₆ andsources connected to the constant current source I₀ and having gatesconnected to an output of an inverter circuit INV4 that receives andinverts a selection signal PH of a control circuit, such as a controlcircuit 102 of FIG. 1. 16 N-channel MOS transistors MN21 ₁ to MN21 ₁₆are switched on or off on by a selection signal PH.

16 N-channel MOS transistors MN22 ₁ to MN22 ₁₆ (switching devices) havedrains connected to the sources of N-channel MOS transistors MN12 ₁ toMN12 ₁₆ and have sources connected to the constant current source I₀,respectively, and having gates connected to and switched on or off by aselection signal PH of a control circuit, such as a control circuit 102of FIG. 1.

A capacitance C is connected across the internal node N31 and the groundGND.

The operation of the internal division in which N (N being 0 to 16, withN=0 denoting no transistor being turned on and N being determined by thecontrol signal PH) of 16 parallel N-channel MOS transistors arc turnedon with the input signal IN1, and in which (16−N) parallel N-channel MOStransistors are turned on after time T with the input signal IN2, withthe sum total of N+(16−N)=16 N-channel MOS transistors being turned onthe whole, is hereinafter explained.

Current flowing through one of parallel N-channel MOS transistors is Iwhich is equal to a current value of the constant current source I₀.

With a threshold voltage V for switching an output of the inverter INV3,an amount of electrical charge required for reaching to the thresholdvoltage is assumed to be CV.

It is assumed that the input signals IN1, IN2 are both at High level, anoutput of the NAND 01 is at Low level and the internal node N31 has beencharged from the power source through the P-channel MOS transistor MP1.It is also assumed that, in this state, the input signals IN1, IN2 fallto the Low level.

First, with N=16, 16 of the 16 N-channel MOS transistors MN11 ₁ to MN11₁₆ are turned on. After time T, 16 parallel N-channel MOS transistorsMN12 ₁ to MN12 ₁₆ are turned off by the input signal IN2 ((16−N)=0)). Asa result, if N=16, the time T (16) until the output of the inverter INV3is inverted after the input signal IN1 goes low isT(16)CV/(16·I)  (3).

With N=n (n<16), where N is set by the control signal PH, n N-channelMOS transistors, the gates of which are fed with an inverted signal ofthe input signal IN1, are turned on during the time T since the inputsignal IN1 falls at Low level, with T being the timing differencebetween the input signals IN1 and IN2, so that n·I·T charges aredischarged.

The input signal IN2 falls at Low level, so that 16−n N-channel MOStransistors, the gates of which are fed with inverted signals of theinput signal IN2, are turned on. Thus, a sum total of the 16 N-channelMOS transistors are turned on.

At a time point T′ when electrical charges left in the internal node N31(CV−n·I·T) are discharged at (16·I), an output of the inverter INV3 isinverted, that is, goes from the High level to the Low level). The timeT′ is given by(CV−n·I·T)/(16·I).

So, time T(n) which elapses since the input signal IN1 falls at Lowlevel until the output of the inverter INV3 is inverted is given byT(n)=(CV−n·I·T)/(16·I)+T/(16·I)+T=CV/(16·I)−(n/T)T+T=T(16)+(16−n)/16)·T  (4).

By a value of n, output signal resulting having a phase that is 16 equaldivision of timing difference T between the input signals IN1, IN2 areobtained. That is, by setting the control signal to vary n, an outputsignal with arbitrarily phase that is divided on a resolution {fraction(1/16)} of the timing difference between the input signals IN1, IN2 areobtained. This interpolator is termed 16-step interpolator.

In general, if an interpolator is to be an M step interpolator, where Mis an optional positive integer, M sets of N-channel MOS transistorsMN11, MN12, MN13 and MN14 are arrayed in parallel.

The input IN1, IN2 of these interpolators are fed with two signals witha timing difference of e.g., 1 clock period tCK, and timing differences0, tCK/16, 2tCK/16, . . . are output from the input IN1 each input clockto generate signals of clock period equal to tCK (1+{fraction (1/16)}).

FIG. 13 illustrates a circuit structure of an interpolator forming thephase adjustment circuit 101 of FIG. 1. Referring to FIG. 13, in thisinterpolator, a plurality of series circuits connected in parallelacross the internal node N31 and the ground are added to the circuitstructure shown in FIG. 12. Each of the series circuits is comprised ofN-channel MOS transistor switches and capacitors. Specifically, theseserial circuits are made up of switching devices MN21 to MN35 andcapacitors CAP11 to CAP 15. The capacitance attached to the internalnode is determined by the control signals connected to the controlterminals of switching devices MN11 to MN15. The capacitors CAP11 toCAP15 are of capacitance values C, 2C, 4C, 8C and 16C, with thecapacitance values added to the internal node being variably determinedby the values of the periodic control signal 7 of the switching devicesMN11 to MN15. The periodic control signal 7 are set from outside andmay, for example, be a control signal 7 supplied from the perioddetection circuit 6 shown for example in FIG. 5.

In the interpolator shown in FIG. 12, the input node N31 is charged tothe power source potential when both the input signals IN1, IN2 are atHigh level, with the internal node N31 being discharged responsive todecay transition of the input signals IN1, IN2 from the High level tothe Low level, with the output signal then rising from Low level to Highlevel. Alternatively, the output signal may rise from Low level to Highlevel responsive to a rise transition from Low level to High level ofthe input signal. For realizing the logic of the output signal going lowfrom high responsive to the fall transition from High level to Low levelof the input signals IN1, IN2, it is sufficient if the inverter INV3 asa reversal buffer is designed as a non-inverting buffer circuit.

FIG. 14 illustrates an alternative circuit structure of an interpolatorforming the phase adjustment circuit 101 shown in FIG. 1. Referring toFIG. 14, the interpolator comprises

a P-channel MOS transistor MP1, having a source and a drain connected toa power source and to the internal node N31, respectively, and having agate fed with an output signal of a NOR circuit NOR 01 fed in turn withthe first and second input signals IN1, IN2, and

an inverter circuit INV3 for switching the logical value of an outputsignal when the relative magnitude of the internal node potential andthe threshold potential value is changed.

The interpolator also includes 16 N-channel MOS transistors MN11 ₁ toMN11 ₁₆ having drains and gates connected in common to the internal nodeN31 and to the input signal IN1, respectively, and

16 N-channel MOS transistors (switching devices) MN12 ₁ to MN12 ₁₆having drains and gates connected in common to the internal node N31 andto the input signal IN2, respectively.

The interpolator also includes 16 N-channel MOS transistors MN21 ₁ toMN21 ₁₆ (switching devices) having drains and sources connected to thesources of N-channel MOS transistors MN11 ₁ to MN11 ₁₆ and to theconstant current source I₀, respectively, and having gates connected toan output of an inverter circuit INV4 and turned on or off. The invertercircuit INV4 is fed with a selection signal PH of a control circuit,such as a control circuit 102 of FIG. 1.

In addition, the interpolator includes 16 N-channel MOS transistors MN22₁ to MN22 ₁₆ (switching devices) having drains and sources connected tothe sources of N-channel MOS transistors MN12 ₁ to MN12 ₁₆ and to theconstant current source I₀, respectively, and having gates connected toand turned on or off by a selection signal PH of a control circuit, suchas a control circuit 102 of FIG. 1.

FIG. 15 illustrates a structure in which a plurality of series circuits,each comprised of N-channel MOS transistor switches and capacitors, andbeing connected in parallel across the internal node N31 and the groundare added to the circuit structure shown in FIG. 14. Specifically, theseserial circuits are made up of switching devices MN21 to MN35 andcapacitors CAP11 to CAP15. The capacitance attached to the internal nodeis determined by the control signals connected to the control terminalsof switching devices MN11 to MN15. The capacitors CAP11 to CAP15 are ofcapacitance values C, 2C, 4C, 8C and 16C, with the capacitance valuesadded to the internal node being variably determined by the values ofthe periodic control signal 7 of the switching devices MN11 to MN15. Theperiodic control signal 7 is set from outside and may, for example, bethe control signal 7 supplied from the period detection circuit 6 shownfor example in FIG. 5.

In circuit configurations of the interpolators shown in FIGS. 12 to 15,locations of transistors MN12 ₁ to MN12 ₁₆ and transistors MN22 ₁ toMN22 ₁₆ may be interchanged and locations of transistors MN11 ₁ to MN11₁₆ and transistors MN21 ₁ to MN21 ₆ may be interchanged. For example,the interpolators shown in FIGS. 12 to 15 may be preferably configuredin such a structure wherein drains of the transistors MN22 ₁ to MN22 ₁₆of which gates are connected in common to the selection signal PH areconnected to the node N31, and drains of the transistors MN12 ₁ to MN12₁₆ of which gates are connected to the input terminal IN2 are connectedrespectively to sources of the transistors MN22 ₁ to MN22 ₁₆ whilesources of the transistors MN12 ₁ to MN12 ₁₆ are connected respectivelyto corresponding current sources I0, and wherein drains of thetransistors MN21 ₁ to MN21 ₁₆ of which gates are connected in common tothe output of the inverter INV4 are connected to the node N31, anddrains of the transistors MN11 ₁ to MN11 ₁₆ of which gates are connectedto the input terminal IN1 are connected respectively to sources of thetransistors MN21 ₁ to MN21 ₁₆, while sources of the transistors MN11 ₁to MN11 ₁₆ are connected respectively to corresponding current sourcesI0.

A further embodiment of the present invention is explained. FIG. 16shows a structure of a fourth embodiment of the present invention,according to which, in the clock control circuit comprised of thefrequency divider 103, phase adjustment circuit 101 and the controlcircuit 102, shown in FIG. 3, the phase adjustment circuit 101 is formedby an interpolator shown in FIGS. 12 to 15.

The interpolator 110 receives a first and second input signals IN1, In2.The first input signal IN1 is a clock signal supplied from a firstD-flipflop 113 that latches with a clock fed to a clock terminalthereof, a signal which is a frequency-divided clock from a frequencydivider 103 that received a clock and is fed to a data input terminalthereof and the second input signal IN2 is a clock signal supplied froma second D-flipflop 114 that latches with a clock fed to a clockterminal thereof, an output signal from the D-flipflop 113.

The interpolator 110 divides timing difference of the first and secondinput signals IN1, IN2 (period tCK of the clocks CLK) with an internaldivision ratio as set by a control signal (selection signal) output by acontrol circuit 102 which comprises an adder 112 that receives the clockand a decoder 111 that decodes an output or the adder 112.

FIG. 17 illustrates a timing waveform diagram for illustrating anexemplary operation of the circuit shown in FIG. 16. The frequencydivider 103 frequency divides the clock. The interpolator 110 iscomprised of the circuit shown in FIG. 14. When the input signals IN1,IN2 are both at Low level, the internal node of the interpolator 110 ischarged. When the input signals IN1, IN2 rise from Low level to Highlevel, the internal node N31 is discharged, such that an output signalOUT, rising at a timing corresponding to division of the timingdifference of the input signals IN1, IN2 (clock period tCK) with theinternal dividing ratio as set by the control signal PH, is output viaan inverter circuit INV3.

Referring to FIG. 17, the signal OUT from the interpolator 110 risesfrom Low level to High level, with a delay ΔΦ as from rising edge of theclock at clock cycle T2.

At clock cycle T4, the input signals IN1, IN2 fed to the interpolatorboth are at Low level, with the internal node N31 being charged to thepower source potential, with the output OUT being at Low level. Thevalue of the control signal PH supplied to the gates of the N-channelMOS transistors MN21 and MN22 is switched, with the signal OUT from theinterpolator 10 rising from Low level to High level after delay of time2ΔΦ from rising edge of the clocks of the clock cycle T6. In this case,the period of the output clock from the interpolator 110 is 4tCK+ΔΦ.

By varying the setting value of the control signal (selection signal ofFIG. 1) supplied to the N-channel MOS transistors MN21 and MN22 of theinterpolator 110 (see FIGS. 12 to 15) at preset timing in one clockcycle of the frequency divided clock, the timing of the output clockrelative to the edge of the input clock (phase difference) may bechanged to convert the frequency.

Another embodiment of the present invention is hereinafter explained.FIG. 18 illustrates a structure of a fifth embodiment of the presentinvention in which an interpolator shown in FIGS. 12 to 15 is used inthe phase adjustment circuit 101 shown in FIG. 1. Referring to FIG. 18,the present embodiment includes D-flipflops 211, 212, two-stage serialcircuits, in which an output of an inverter INV that receives an outputsignal of the back stage D-flipflops 212 is fed back to a data terminalD of the frond stage D-flipflops 211, and first to fourth D-flipflops213 to 216, connected in a cascade to form a shift register, fed with anoutput of the D-flipflop 212 as an input.

The present fifth embodiment also includes a first interpolator 217, fedwith outputs Q1, Q2 of the first and second flipflops 213, 214 as inputsand outputting a signal of the time delay corresponding to the divisionof the timing difference T, a second interpolator 218, fed with outputsQ2, Q3 of the second and third flipflops 214, 215 as inputs andoutputting a signal of the time delay corresponding to the division ofthe timing difference T, a third interpolator 219, fed with outputs Q3,Q4 of the third and fourth flipflops 215, 216 as inputs and outputting asignal of the time delay corresponding to the division of the timingdifference T, and a fourth interpolator 219, fed with outputs Q4, Q1 ofthe fourth and first flipflops 216, 213 as inputs and outputting asignal of the time delay corresponding to the division of the timingdifference T. The first to fourth interpolators 217 to 220 are fed witha control signal 222, setting the internal division ratio of the timingdifference, from a control circuit, not shown.

The value of the control signal 222 supplied to the first to fourthinterpolators 217 to 220 may be fixed without being changed on the clockbasis.

FIG. 19 illustrates a typical operation of the circuit shown in FIG. 18Referring to FIG. 19, the first interpolator 217 outputs an outputsignal obtained on division of the timing difference tCK of the signalsQ1, Q2 (with a timing difference ΔΦ from the rising edge of the clock ofthe clock cycle T2). The second interpolator 218 outputs an outputsignal obtained on division of the timing difference tCK of the signalsQ2, Q3 (with a timing difference 2ΔΦ from the rising edge of the clockof the clock cycle T2). The third interpolator 219 outputs an outputsignal obtained on division of the timing difference tCK of the signalsQ3, Q4 (with it timing difference 3ΔΦ from the rising edge of the clockof the clock cycle T4). The fourth interpolator 220 outputs an outputsignal obtained on division of the timing difference tCK of the signalsQ4, Q1 (with a timing difference 4ΔΦ from the rising edge of the clockof the clock cycle T2=beginning of the clock period tCK). In this case,the interpolator outputs clocks with a period of tCK(1+¼) for an inputclock (clock period tCK).

The first to fourth interpolators 217 to 220 may output the resultscalculated by a logic circuit depending on the application, orselectively output the result via a selector. The present invention maybe applied with advantage to a rate conversion circuit in e.g., mBnB (mbits n bits) coding system.

A further embodiment of the present invention is hereinafter explained.FIG. 20 illustrates a structure of a sixth embodiment of the presentinvention. Referring to FIG. 20, the present embodiment includes aninterpolator for frequency-multiplication 10, a switch (rotary switch)20, an interpolator 30, also called a fine adjustment interpolator, anda control circuit 40.

The interpolator for frequency-multiplication 10 generatesmultiple-phase frequency-multiplication clocks P0 to Pn from the inputclock 1. The interpolator for frequency-multiplication 10 is configuredas shown in FIG. 5.

The switch 20 selects two of the clocks from the multiple-phasefrequency-multiplication clocks P0 to Pn to furnish the selected clocksas two input signals to the fine adjustment interpolator 30.

The control circuit 40 furnishes control signals S for the switch 20 andthe fine adjustment interpolator 30 and the PH (control signal furnishedto the gates of the N-channel MOS transistors 21, 22 of the interpolator30). The control circuit 40 includes an adder, not shown, fed withclocks 1, and a decoder, not shown, for decoding an output of the adderto output the control signals D and the PH.

The switch 20 selects odd-phased signal and even-phased signal,neighboring to each other, based on the control signal S from thecontrol circuit 40 to furnish the selected clock pair to theinterpolator 30, which then outputs, based on the control signal fromthe control circuit 40, a signal of the phase corresponding to theinternal division of the phase difference (timing difference) of the twoinputs. In the present embodiment, the interpolator 30 is configured asshown in FIGS. 12 to 15.

FIG. 21 Illustrates a typical operation for a case wherein theinterpolator 30 is constructed by a circuit shown in FIG. 15 and whereinthe interpolator for multiplication 10 (see FIG. 5) generates four-phasemultiplication clocks P0 to P3.

The rotary switch 20 cyclically selects multi-phase clocks, from themulti-phase clocks P0 to P3, in the order of, for example, (P0, P1),(P1, P2), (P2, P3), (P3, P0), (P0, P1), . . . With the period of themulti-phase clocks T, the switch 20 selects P0, P1 at a clock cycle T1,whilst the interpolator 30 is responsive to the rising of P0, P1 toissue an output signal OUT. At a cycle T2, the switch 20 selects P1, P2,while the interpolator 30 is responsive to the rising of P1 and P2 tooutput an output signal OUT at a timing of time (1+¼) as from the risingedge of the previous output signal OUT. In similar manner, the switchselects P3 and P4, followed by P4, P1, to output clocks with the periodT (1+¼).

In the embodiment shown in FIG. 21, the interpolator is outputtingclocks with a period (1+¼)T5T/4 for the period T of the multiplicationclocks, with the frequency being ⅘ times that of the clock period. Ifthe interpolator for multiplication 10 is multiplying the input clock bya factor of 2m, the frequency of the output clocks is multiplied by afactor of 8m/5.

A further embodiment of the present invention is hereinafter explained.FIG. 22 shows the structure of a seventh embodiment of the presentinvention. Referring to FIG. 22, the seventh embodiment of the presentinvention is a modification of the structure shown in FIG. 20. That is,a rotary switch 20 outputs two sets of paired clocks which are fed tofirst and second interpolators 30 ₁, 30 ₂, outputs of which are fed to athird interpolator 10 ₃ as inputs. Output clocks are obtained from anoutput of the third interpolator 10 ₃.

In the present embodiment, the ratio of the internal division of thetiming difference of the respective interpolators of the first to thirdinterpolators 30 ₁ to 30 ₃. Alternatively, responsive to the timingaccuracy as found by the application, the ratio of internal division ofthe timing difference of the interpolator 30 ₁ may be fixed while thatof the interpolators 30 ₂, 30 ₃ may be varied by the control signalsfrom the control circuit 40. Still alternatively, the ratio of theinternal division of the interpolators 30 ₂, 30 ₃ may be varieddepending on the control signal from the control circuit 40. The ratioof the internal division of the timing difference of the interpolators30 ₁, 30 ₂ may be fixed, while that of only the last stage interpolator30 ₁ may be varied with the control signal from the control circuit 40.

In a seventh embodiment of the present invention, the fine adjustmentinterpolators 30 are arranged in a multi-stage configuration, indistinction from the structure shown in FIG. 20, whereby the ratio ofthe internal division of the timing difference may be set to a finervalue. In case the second and third interpolators 30 ₂, 30 ₃ arearranged as 16 equi-divisional interpolators, the timing difference maybe internally divided to a resolution of {fraction (1/256)}.

An eighth embodiment of the present invention is hereinafter explained.In FIG. 23, showing a modification of the configuration shown in FIG. 3,clocks are frequency divided by a frequency divider 60 to output twopaired clocks which are furnished to the first and second interpolators30 ₁, 30 ₂. Output clocks are derived from an output of the thirdinterpolator 30 ₃, fed as input with the outputs of the twointerpolators 30 ₁, 30 ₂.

A ninth embodiment of the present invention is hereinafter explained.Referring to FIG. 24, the ninth embodiment of the present invention is amodification of the embodiment shown in FIG. 18, and includes aninterpolator for frequency-multiplication 10 for generating first to nthclocks P1 to Pn (n-phased multiplication clocks) of respectivelydifferent phases, obtained on multiplication of the input clock, firstto nth interpolators 30 ₁ to 30 _(n), and a synthesis unit 50 fed withoutputs of the first to nth interpolators 30 ₁ to 30 _(n) (fineadjustment interpolators) to multiplex the input signals to unify thesignals to output a sole output signal OUT. The first to nthinterpolators 30 ₁ to 30 _(n) are fed with two clocks of neighboringphases of the first to nth clocks P1 to Pn from the interpolator formultiplication 10 to output a signal corresponding to division byrespectively different ratios of internal division of the timingdifference of the two input signals.

The first to nth interpolators 30 ₁ to 30 _(n) are configured as shownin FIGS. 12 to 15 to divide the timing difference T of the two inputsignals by m steps, where n≦m. With the interpolator for multiplication10 and fine adjustment interpolator 30 for generating the n-phasedmultiplication clocks, it is possible to generate the timingcorresponding, to division by n×m steps as output signal OUT.

In the embodiment shown in FIG. 24, similarly to the configuration shownin FIG. 18, the interpolator 30 ₁ fed with neighboring ith and (i+1)stclocks of the n-phase clocks, as inputs, where i is an integer from 1 ton, with the (n+1)st clock being the first clock P1), and theinterpolator 30 _(i−1) with the (i−1)st and Pith clocks as inputs, areset so that the values of the ratio of the internal division of thetiming difference thereof will differ from each other. Specifically, thedelay time of the interpolator 30 ₁ is larger than that of theinterpolator 30 _(i−1).

The synthesis unit 50 for multiplexing outputs of the first to nthinterpolators 30 ₁ to 30 _(n) for outputting an output signal OUT ismade up of a pulse width correction circuit 4 c and a multiplicationcircuit 4 b.

In the configuration of FIG. 24, the configuration of generating M-phaseclocks (M multiplication clocks) from the n-phase multiplication clocks,output from the interpolator for multiplication 10, is explained. Inthis case, M interpolators are arranged in parallel, where M≦N.

In this case, the ith interpolator 30 _(i) is fed with neighboring ithand (i+1)st clocks, where i is an integer from 1 to M and the (n+1)stclock is the first clock P1. The values of the ratio of the internaldivision prescribing the division positions of the timing differencebetween the two input signals in the respective interpolators 30 are setas the values are sequentially shifted from the leading end towards thetrailing end of the timing domain, each unit step m, in the increasingsequence of the interpolator numbers, such as,

for the 1st interpolator 30 ₁, the internal division ratio m; M−m,

for the 2nd interpolator 30 ₂, the internal division ratio 2m;M−2m,

for the 3rd interpolator 30 ₃, the internal division ratio 3m;M−3m.

Alternatively, the division positions of the timing difference T may beset as the values are sequentially shifted from the trailing end towardsthe leading end of the timing domain, each unit step m, in theincreasing sequence of the interpolator numbers.

This setting may be achieved by controlling the on/off of the N-channelMOS transistors MN21 and MN22, with the control signal PH supplied tothe interpolator, as explained with reference to FIGS. 12 to 15. In thepresent embodiment, the value of the ratio of the internal division ofeach interpolator is fixed.

From the synthesis unit 50, multiplexing the outputs of the minterpolators 30 to a sole output signal OUT, M-tupled clocks may beproduced. For example, with m=1 for n=8 and M=7, seven-phased clocks maybe generated from the eight-phase clocks (eight-phased clocks) outputfrom the interpolator for multiplication 10. From the synthesis unit 50,fed with the seven-phased clocks, 7-tupled(multiplied by 7 in frequency)clock is output.

FIG. 25 illustrates an example of a layout of an integrated circuit of a16-equi-division interpolator.

FIG. 26 shows waveforms obtained by a circuit simulation of a phaseadjustment circuit employing a fine adjustment interpolator. Phasedifference of 625 MHZ is divided into 16 equal portions by a16-equal-dividing interpolator and five phases of the phase changeoverportion are shown. The fine adjustment phase difference is 12.5 ps.

In the above-described embodiment of the present invention, in which theinterpolators are arrayed in plural stages, the timing edge of an outputsignal can be controlled to an order of 10 psec. That is, the presentinvention is applicable not only to a clock frequency conversion circuitor a clock synchronization circuit but also to a pattern generator or atiming generator in a measurement and testing device. For example, thepresent invention may be used with advantage in a timing generator foran LSI tester in which the timing is variably set on-the-fly.

The configuration having a frequency divider and a phase adjustmentcircuit (interpolator for phase adjustment) as explained with referenceto FIGS. 3 and 23, for example, may be applied to a frequency divider ina PLL (phase locked loop) having a charge pump for generating thevoltage corresponding to the phase difference of the phase comparator, aloop filter, a VCO (voltage-controlled oscillator) fed with an output ofthe loop filter as a control voltage and a frequency dividing circuitfor supplying a signal obtained on frequency division of the VCO outputto the phase comparator.

The meritorious effects of the present invention are summarized asfollows. According to the present invention, as described above,non-integer frequency conversion may be achieved to high precisiondespite a simpler structure.

The reason is that such a configuration is used in the present inventionin which the phases of the signals output from the phase adjustmentcircuit fed with clocks as inputs may be summed or subtracted by unitphase difference on the clock basis.

According to the present invention, there is provided on feedbacksystem, not jitter proper to the feedback system, thus enablinghigh-speed clock synchronization. It should be noted that other objects,features and aspects of the present invention will become apparent inthe entire disclosure and that modifications may be done withoutdeparting the gist and scope of the present invention as disclosedherein and claimed as appended herewith.

Also it should be noted that any combination of the disclosed and/orclaimed elements, matters and/or items may fall under the modificationsaforementioned.

1. A clock control circuit comprising: a multi-phase multiplicationclock generating circuit receiving an input clock to generate aplurality of clocks of respective different phases (termed multi-phasemultiplication clocks) obtained on multiplying the input clock; aplurality of interpolators receiving respectively two clocks ofneighboring phases of said plural clock outputs from said multi-phasemultiplication clock generating circuit to output signals correspondingto division with respective different values of the ratio of internaldivision of the timing difference of said two clocks; and a synthesisunit fed with outputs of said plural interpolators to multiplex saidoutputs from said plurality of interpolators to output as resulting soleoutput signal.
 2. The clock control circuit as defined in claim 1wherein said multi-phase multiplication clock generating circuitgenerates N phase clocks, where N is a preset positive integer, M ofsaid interpolators are provided, where M is a positive integer, suchthat M≦N an ith one of said interpolators is fed with ith and (i+1)stclocks, where i is an integer from 1 to M, with the (n+1)st clock beinga first clock; a value of a ratio of the internal division dividing thetiming difference of two input signals in each of said interpolatorbeing so set that a ratio value of the (i+1 )st interpolator is largeror smaller than that of the ith interpolator by a preset unit step;M-phase clocks being output from said M interpolators; and wherein anoutput clock of a multiplied by M frequency is output from saidsynthesis unit.
 3. A clock control circuit comprising: a clockgenerating circuit that generates a set of multi-phase clocks; and aplurality of interpolators receiving respectively two clocks ofneighboring phases of said multi-phase clocks to output signalscorresponding to division with respective different values of the ratioof internal division of the timing difference of said two clocks.